Method for the manufacture of centrifugal castings

ABSTRACT

A METHOD FOR THE MANUFACTURE OF CENTRIFUGAL CASTINGS IN WHICH THE MELT CONTAINS MORE THAN 4 PERCENT BY WEIGHT OF CARBON AND THE CASTING TAKES PLACE AT INCREASED TEMPERATURES AND/OR CENTRIFUGAL VELOCITIES.

p 26. m2 M. MIRJANIC 3,694,194

METHOD FOR THE MANUFACTURE OF CENTRIFUGAL CASTINGS Filed Sept. 15, 1969 ILaRA 0 MIR TANIC W'IMQ/NQI United States Patent 3,694,194 METHOD FOR THE MANUFACTURE OF CENTRIFUGAL CASTINGS Milorad Mirianic, Fellbach, Wurttemberg, Germany, as-

signor to Daimler-Benz Aktiengesellschaft, Stuttgart- Unterturkheim, Germany Filed Sept. 15, 1969, Ser. No. 857,815 Claims priority, application Germany, Sept. 14, 1968, P 17 83 002.3 Int. Cl. B22d 13/02; C22c 37/00 US. Cl. 75130 R 6 Claims ABSTRACT OF THE DISCLOSURE A method for the manufacture of centrifugal castings in which the melt contains more than 4 percent by weight of carbon and the casting takes place at increased temper atures and/ or centrifugal velocities.

The present invention relates to a method for the manufacture of centrifugal castings, especially of cylinder liners made from cast-iron having a high carbon content.

In the manufacture of bearing boxes or hearing sockets or cylinder liners or the like from centrifugal casting, cast iron is used to date which contains a maximum of 3.8 percent by weight of carbon. By the addition of alloys is achieved that about 0.8 percent of the carbon is combined in the form of cementite or iron carbide whereas about 3 percent remains in the structure as graphite. These quantities of graphite, however, do not suffice in most cases to fully utilize the known, advantageous influence of the graphite with respect to the emergency operating characteristics of castings. However, heretofore, it was not possible to accommodate or store more than 3 percent carbon as graphite in the structure since percentages exceeding the same were separated out at the surfaces of the castings. Additionally, it is disadvantageous that the carbon present in the structure separates out or precipitates, for the most part, in the form of spheroidal graphite which is not particularly favorable for the improvement of the emergency running characteristics because it is not securely connected with and bound in the surrounding structure but, instead, during operation, is readily detachable for the most part by breaking or flaking out.

The present invention is predicated on the aim to avoid the aforementioned shortcomings and to enable by a special method of the aforementioned type, the manufacture of cast iron saturated with graphite. The present invention essentially consists in that the melt possesses a carbon content of over 4 percent by weight and the casting takes place at increased temperature of the melt and/or increased centrifugal velocity. The mechanical casting conditions are so changed by the method in accordance with the present invention that it becomes possible to enrich and to supersaturate the cast iron with graphite to a farreachingly greater extent than heretofore possible. Additionally, the surprising advantage results in connection therewith that the graphite is present in the structure in lamellar form and, as a result thereof, is connected with or bound to the same particularly securely.

In order to improve the casting conditions, known, conventional alloy elements may be admixed to the melt which are so selected that the melt solidifies pearlitically and the graphite formation is enhanced in the structure. Particularly, a reduction of the silicon components and a reduction of the manganese components favor the graphite formation.

According to a further feature of the present invention, it may be advantageous, in order to increase again the tensile strength reduced by the high graphite content,

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to admix to the cast iron known, conventional alloy elements for increasing the tensile strength. For example, copper and nickel or also molybdenum are suitable therefor.

A special distribution of the graphite is also achieved by the change of the mechanical or physical casting conditions according to the present invention in that the interior wall is enriched more strongly with graphite than the external wall. This is advantageous in particular for hearing sockets and cylinder liners since the the bearing surfaces thereof are located at the inner Walls enriched with high graphite content in lamellar form. The cause for this distribution is apparently both the smaller viscosity of the melt conditioned by the higher temperature as also the larger centrifugal force which, each by itself or even more effectively, both together, effect that during the manufacture of centrifugal castings, the more heavy iron particles always migrate more strongly toward the outside.

The normal temperature of the melt as used at present for centrifugal castings of the type described above amounts to about 1550 Celsius. According to the present invention, the method is to be carried out at a temperature above this conventional temperature, preferably at a temperature of 1650- *-30 Celsius.

Centrifugal velocities are normally expressed in r.p.m.s (number of rotations per minute), depending on the diameter of the part to be made, e.g of a cylinder to be cast. For a cylinder of up to mm. outer diameter, a rotational speed for the mold of such cylinder of about 1300 r.p.m. is standard at present. The present invention contemplates a rotational speed of the mold in excess thereof, and more particularly within a range from about above 1300-4000 r.p.m. For the cylinder outer diameter indicated above, the present invention prefers a rotational speed of about 14004650 r.p.m.

Typical characteristic values for cylinder liners made in accordance with the present invention are as follows:

Analysis (in percent by weight) Carbon content 4.5 to 5.0%. Combined carbon 0.7 to 0.9%. Graphite 3.6 to 4.3%. Manganese 0.1%. Silicon 1.2 to 1.3%. Phosphorus 0.3%. Sulfur (0.01%. Nickel Approximately 1%. Copper 1.2 to 1.3%.

Vickers Hardness HV 0.05 (in kg./mm. A hardness range between about 250-350 kg./mm.

Tensile strength A tensile strength 18 kg./mm. notwithstanding the desired high carbon content, realized by the admixture of approximate amounts of suitable alloy components, such as Cu and Ni in the proportions indicated above though the admixture of molybdenum in amounts of about 0.7- 1% and of other alloying elements with similar properties is also feasible. Obviously, the amounts of alloying components may vary substantially, as known to those skilled in the art, depending on the tensile strength in the centrifugally cast part which one seeks. Furthermore, other conventional alloying components producing an increase in tensile strength may also be used within the scope of the present invention since the effects of such admixtures are known to those skilled in the art and produce substantially similar results in the castings of this invention as obtained with similar castings of the prior art insofar as increases in tensile strength are concerned.

Arrangement of structure Liner N0. 1

Liner No. 2

PPPPPFPPP woooom or oquseeog tc e PPPPPEPP owooowocme rewms gooeeeew B 1 fi 3 'r"7" rne ar ness, g.mm

Futurerunning surface..-" 154 166 154 142 142 136 127 136 Core 219 238 238 241 151 160 154 157 Outer wall 249 238 249 249 181 178 187 157 Microsection:

Matrix Vicker Hardness HV 0.0 kg.

Future running surface 321 396 280 362 271 321 310 271 321 332 286 396 303 Outer wall 303 313 313 286 332 296 280 286 1 Lamellar graphite 145-6 and some carbon-temper-like graphite W3- 2 Very wide lamellar graphite 114-6.

3 Lamellar graphite 144 6.

4 Lamellar graphite AIS-6.

5 Eutectic graphite D8.

6 Eutectic graphite D7-8.

7 Lamellar graphite 114-6 and carbon-temper-hke graphite W3-4.

E Lamellar graphite 113-5 in very wide form.

9 Lamellar pearlite, in the eutectic zone very fine pearlite and some ferrite, little phosphide deutectieum.

Lamellar pearlite, very little phosphide deutecticurn.

The method according to the present invention of centrifugally casting parts of the type described above takes place in a conventional manner except for the increase in rotational speed and/or temperature as indicated above.

The accompanying drawing illustrates photomicrographs of the structure at the future running surface of centrifugal-castings made in accordance with the present invention, wherein:

PEG. 1 is a photomicrograph (100:1 magnification) of the inner side of a first specimen of a non-alloyed cylinder liner made in accordance with the present invention;

FIG. 2 is a photomicrograph (200:1 magmfication) of the specimen shown in FIG. 1;

FIG. 3 is a photomicrograph (100:1 magnification) of the inner side of a second specimen of an alloyed cyhnder liner made in accordance with the present invention; and

FIG. 4 is a photomicrograph (200:1 magnification) of the specimen shown in FIG. 3.

I claim:

1. A method for producing a centrifugal casting of castiron having a pearlitic matrix in which more than 4 percent by weight of carbon is present predominantly in lamellar form as graphite, which comprises forming a castiron melt with a carbon content of over 4 percent by weight, admixing conventional alloying elements with said melt to be cast so that a melt solidifies pearlitically with enhanced graphite formation and with increased tensile strength, and centrifugally casting the melt under such casting conditions that at least the temperature of the melt is increased to be in the range of about 1620 C. to 1680 C. or the centrifugal velocity is increased to be in the range of about 1300 to 4000 revolutions per minute for a casting having an outer diameter up to 100 mm.

2. A method according to claim 1, characterized in that the temperature of the melt and the centrifugal velocity are each increased.

3. A method according to claim 2, characterized in that the temperature of the melt and the centrifugal velocity are so selected that the resultant cast structure has an inner wall enriched more strongly with graphite than the outer wall.

4. A method according to claim 2, characterized in that conventional alloying elements for the increase of the tensile strength are admixed to the cast iron.

5. A method according to claim 1, characterized in that the casting conditions are so selected that the cast structure is supersaturated with said graphite and free ferrite only occurs in negligible quantities.

6. A method according to claim 1, characterized in that additional conventional alloying elements for the increase of the tensile strength are admixed to the cast iron.

References Cited UNITED STATES PATENTS 1,702,128 2/ 1929 Niedringhaus 14835 1,871,544 8/1932 McCarroll 148-35 X 2,689,990 9/1954 Samuels l4835 X 3,559,775 2/ 1971 Miller. 148-35 X 1,793,268 2/ 1931 Williams -58 2,731,690 l/ 1956 Coupland, Jr., et al. 1641 14 X 3,415,307 12/1968 Schuh et al. 164114 3,563,300 2/1971 Honda et a1 164-1 14 X L. DEWAYNE RUTLEDGE, Primary Examiner J. E. LEGRU, Assistant Examiner US. Cl. X.R.

75123 CB; 148-35; l64-114 

